Lateral collection architecture for SLS detectors

Abstract

Lateral collection architecture for a photodetector is achieved by depositing electrically conducting SLS layers onto a planar substrate and diffusing dopants of a carrier type opposite that of the layers through the layers at selected regions to disorder the superlattice and create diode junctions oriented transversely to the naturally enhanced lateral mobility of photogenerated charge carriers within the superlattice. The diode junctions are terminated at a top surface of the photodetector within an SLS layer of wide bandgap material to minimize unwanted currents. A related architecture disorders the superlattice of topmost SLS layers by diffusing therethrough a dopant configured as a grid and penetrating to a lower SLS layer having the same carrier type as the dopant and opposite that of the topmost layers to isolate pixels within the topmost layers. Ohmic contacts may be deposited on doped regions, pixels, and substrate to provide desired external connections.

What is claimed is: 
     
       1. A method for fabricating a photodetector array having lateral collection architecture, comprising:
 providing a substrate suitable for depositing thereon one or more photosensitive layer structures; 
 depositing on the substrate a first electrically conducting layer having a single carrier type; 
 depositing on the first electrically conducting layer a second electrically conducting layer of a photosensitive quantum confined detector material having the same carrier type as the first electrically conducting layer; 
 masking the second electrically conducting layer to locate unmasked regions for conversion; 
 forming an anisotropic cavity in the second electrically conducting layer at the unmasked regions prior to diffusing a dopant into the anisotropic cavity; 
 converting at least a portion of a surface and at least a portion of a near surface part of the unmasked regions to doped regions having a carrier type opposite that of the first and the second electrically conducting layers; 
 masking the doped regions to define locations for deposition of first Ohmic contacts on each of the doped regions; 
 depositing the first Ohmic contacts on the locations defined in the previous step; and 
 providing electrical connections to the first Ohmic contacts, and to the first electrically conducting layer via a second Ohmic contact. 
 
     
     
       2. The method of  claim 1  wherein the converting step comprises converting at least the portion of the surface and at least the portion of the near surface part of the unmasked regions by ion implantation. 
     
     
       3. The method of  claim 1  wherein the converting step comprises converting at least the portion of the surface and at least the portion of the near surface part of the unmasked regions by diffusing a dopant into the second electrically conducting layer. 
     
     
       4. The method of  claim 1  wherein the doped regions comprise a homogeneous quaternary. 
     
     
       5. A method for fabricating a photodetector or photodetector array, comprising:
 providing a substrate suitable for depositing thereon one or more photosensitive layer structures; 
 depositing on the substrate a first electrically conducting layer having a single carrier type; 
 depositing a second electrically conducting layer of a photosensitive quantum confined detector material, the second electrically conducting layer having the same carrier type as the first electrically conducting layer; 
 depositing a third electrically conducting layer of a photosensitive quantum confined detector material, the third electrically conducting layer having a single carrier type of a type opposite the first electrically conducting layer; 
 depositing a fourth electrically conducting layer having a wider bandgap than the third electrically conducting layer and having a same carrier type as the third electrically conducting layer; 
 masking the fourth electrically conducting layer to locate pixels between unmasked regions; 
 forming an anisotropic cavity in the second electrically conducting layer at the unmasked regions prior to diffusing a dopant into the anisotropic cavity; 
 converting at least a portion of a surface and at least a portion of a near surface part of the unmasked regions to doped regions, each doped region having the carrier type of the first and the second electrically conducting layers to a depth penetrating to the second electrically conducting layer; 
 masking the fourth electrically conducting layer to define locations for deposition of first Ohmic contacts on each of the pixels; 
 depositing the first Ohmic contacts on surfaces of the pixels; and 
 providing electrical connections to the first Ohmic contacts, and to the first electrically conducting layer via a second Ohmic contact. 
 
     
     
       6. The method of  claim 5  wherein the converting step further comprises modifying chemical and, physical properties of the unmasked regions to create the pixels, each pixel formed from the third and the fourth electrically conducting layers and isolated from all other pixels by the doped regions and by the second electrically conducting layer. 
     
     
       7. The method of  claim 5  wherein the third and the fourth electrically conducting layers comprise strained layer superlattice structures and wherein the converting step comprises disordering the superlattice structures to form a homogeneous quaternary. 
     
     
       8. The method of  claim 7  further comprising disordering the superlattice structures by ion implantation. 
     
     
       9. The method of  claim 5  wherein the anisotropic cavity is formed through the fourth electrically conducting layer at each of the unmasked regions, and the dopant is diffused into the anisotropic cavity. 
     
     
       10. The method of  claim 5  wherein the forming step further comprises forming anisotropic cavities by plasma etching. 
     
     
       11. A method for fabricating a cap-doped photodetector pixel array having a wide bandgap passivation layer, comprising:
 providing a substrate suitable for depositing a photosensitive layer structure thereon; 
 forming on the substrate an electrically conducting layer of a photosensitive quantum confined detector material having a single carrier type; 
 delineating a plurality of mesas from the electrically conducting layer, the plurality of mesas extending into or through the photosensitive layer; 
 converting a layer on top of each mesa and along at least a part of sidewalls of each mesa that extends at least through some distance along an exposed side of the photosensitive layer to a material having a carrier type opposite that of the electrically conducting layer, thereby enhancing lateral collection of minority carriers; 
 masking top surfaces of the mesas to define unmasked locations for deposition of Ohmic contacts; 
 depositing Ohmic material on the unmasked locations; and 
 providing electrical connections to the Ohmic contacts and to the substrate. 
 
     
     
       12. The method of  claim 11  wherein the converting step comprises ion implantation or diffusion. 
     
     
       13. The method of  claim 11  wherein the converted layer extends along a base of each mesa. 
     
     
       14. The method of  claim 11  wherein the converted layer is a quaternary formed separately or using the step of converting the layer on top of each mesa and along at least the part of sidewalls of each mesa. 
     
     
       15. A method for fabricating a photodetector or photodetector array, comprising:
 providing a substrate suitable for depositing thereon one or more photosensitive layer structures; 
 depositing on the substrate a first electrically conducting layer having a single carrier type; 
 depositing a second electrically conducting layer of a photosensitive quantum confined detector material, the second electrically conducting layer having the same carrier type as the first electrically conducting layer; 
 depositing a third electrically conducting layer of a photosensitive quantum confined detector material, the third electrically conducting layer having a single carrier type of a type opposite the first electrically conducting layer wherein the third electrically conducting layer comprises a strained layer superlattice structure; 
 depositing a fourth electrically conducting layer having a wider bandgap than the third electrically conducting layer and having a same carrier type as the third electrically conducting layer wherein the fourth electrically conducting layer comprises a strained layer superlattice structure; 
 masking the fourth electrically conducting layer to locate pixels between unmasked regions; 
 converting unmasked regions to doped regions, each doped region having the carrier type of the first and the second electrically conducting layers to a depth penetrating to the second electrically conducting layer; 
 masking the fourth electrically conducting layer to define locations for deposition of first Ohmic contacts on each of the pixels; 
 depositing the first Ohmic contacts on surfaces of the pixels; and 
 providing electrical connections to the first Ohmic contacts, and to the first electrically conducting layer via a second Ohmic contact. 
 
     
     
       16. The method of  claim 15  wherein the converting step further comprises modifying chemical and physical properties of the unmasked regions to create the pixels, each pixel formed from the third and the fourth electrically conducting layers and isolated from all other pixels by the doped regions and by the second electrically conducting layer. 
     
     
       17. The method of  claim 15  further comprising disordering the superlattice structures to form a homogeneous quaternary. 
     
     
       18. The method of  claim 15  further comprising forming an anisotropic cavity in the second electrically conducting layer at the unmasked regions prior to diffusing a dopant into the anisotropic cavity. 
     
     
       19. The method of  claim 15  wherein the forming step further comprises forming anisotropic cavities by plasma etching.